Papermaker's felts are used in the press section of a papermaking machine to extract water from the wet paper web. The paper web is supported on the felt and passes through the nip between a pair of cooperating press rolls to extract water from the web. It is recognized that when the felt and supported paper web are released from the nip, the felt and paper will tend to expand to their original thickness and this expansion sets up hydraulic and capilliary forces, which tends to draw water from the felt back into the paper web, a phenomenon commonly referred to as "rewetting".
It has been proposed in the past to incorporate a layer of open cell polymeric foam as a component of a papermaker's felt. For example, U.S. Pat. No. 3,059,312, discloses a papermaker's felt composed of a base fabric, and a layer of an open cell polymeric foam sandwiched between the base fabric and an outer fibrous batt. The batt is then needled to the base fabric to provide the felt structure.
U.S. Pat. No. 3,617,442, is directed to a structure to be used as a papermaker's felt or a forming wire, in which the endless structure is composed solely of an open cell polymeric material. When used as a forming wire, the polymeric material can also be reinforced by internal machine direction yarns.
The prior felt constructions incorporating a polymeric foam layer, have utilized an open cell foam, in which the cells or pores are interconnected to provide a water permeable structure. Closed cell polymeric foam has not been recognized as a viable component in a papermaker's felt because the foam is substantially impervious to the flow of fluids. This is true even though open cell foam is considerably more expensive than closed cell foam due to the fact that open cell foam is produced by costly chemical and/or mechanical reticulating processes.